Modular wireless fixed network for wide-area metering data collection and meter module apparatus

ABSTRACT

A one-way direct sequence spread spectrum (DSSS) communications wide-area network is the data collection channel (uplink) of an automatic meter reading (AMR) system, and a paging network, or other suitable communication channel is the optional forward (downlink) channel. The communications network may include one-way meter modules (transmitters) each communicatively coupled to a corresponding electric, gas or water utility meter, and may include two-way meter modules (transceivers) each coupled to such a corresponding utility meter. The meter modules monitor, store, encode and periodically transmit metering data via radio signals (air messages) in an appropriate RF channel. Metering data air messages are collected by a network of receiver Base Stations (BS) and forwarded to a Data Operations Center (DOC), which acts as a metering data gateway. The reception range of each base station is typically over 5 miles in urban areas, allowing sparse infrastructure deployment for a wide variety of metering data collection applications.

This application is a divisional of nonprovisional application Ser. No.10/199,108 filed Jul. 22, 2002 now U.S. Pat. No. 7,012,546; which is aCIP of U.S. patent application Ser. No. 09/950,623 filed on Sep. 13,2001 now U.S. Pat. No. 7,009,530.

FIELD OF THE INVENTION

The present invention generally relates to wireless messaging systemsand methods. In particular, the present invention relates to wirelessmessaging systems and methods for automated meter reading (AMR) andmetering data collection.

BACKGROUND

Automated Meter Reading (AMR) was developed as a more efficient andaccurate method for utility meter data collection, as compared to priormanual meter reading of electric, gas and water meters, and severalimportant advantages of AMR over manual meter reading helped develop itinto a specialized branch of the data communications and telemetryindustry. Worth noting among these advantages are the reliability,accuracy and regular availability of such metering data, which may becollected from hard-to-reach meter locations as well as from standardmeter locations; higher customer security (no need to enter homes) andsatisfaction (accurate bills); and reduced cost of customer service callcenter and service house calls for settling billing disputes.

Various technologies have been used in previous AMR systems to performthe tasks of interfacing the meter in order to sense consumption,communicating consumption data to a central site, and storingconsumption data in a computer system at the central site. Wirelesstechnologies, which have become the most common in AMR systemimplementation due to the ease of the installation process and, in manycases, the low initial and operating costs of the system, include bothmobile data collection systems and fixed-base data collection systems,or networks. Although both provide a more reliable method of collectingmonthly meter reads for billing purposes, fixed networks have somedistinct, and important, advantages, brought about by the capability ofsuch systems to provide frequent (typically at least daily) consumptiondata collection, which is difficult to do with typical mobile systems.Other advantages include: flexibility of billing date; marketing toolssuch as time-of-use (TOU) rates, demand analysis and load profiling,which enable clearer market segmentation and more accurate forecasts forutility resource generation, and also serve the goal of energyconservation and efficient consumption; and maintenance tools such asimmediate notification of utility resource leakage or of accountdelinquency. These advantages have triggered increased interest andcommercial activity regarding fixed network data collection systems forutilities, particularly utilities in regions undergoing deregulation ofutility services.

Several methods and systems for implementing fixed-base data collectionfrom a plurality of remote devices, such as utility meters, to a centrallocation, have been developed and introduced in the past years. Acategorization has evolved within the AMR industry, generallydifferentiating between one-way and two-way wireless data networks. Somesystems require that each meter module on the network be a two-waymodule, i.e. contain a receiver circuit in the meter module. Althoughtwo-way communication features such as on-demand meter reading and otherremote commands for meter configuration and control are generallydesirable, they may not be required for the entire meter population of autility. Since the inclusion of a receiver in the meter modulecontributes significant cost to the module, it would be most desirableto allow a utility service company the flexibility to deploy an AMRnetwork which may contain and support both one-way and two-way metermodules.

One-way (collection only) data networks can support the large volume ofdata expected with the use of advanced metering applications, as bydeploying intermediate data collection nodes, each of which creates asmall data collection cell with a short-range RF link and a typicalservice population of several hundreds of meters. In such networks, theintermediate data collection nodes receive messages from meter modules,perform metering data analysis, and extract, or generate, specific meterfunction values to be transmitted to the next level in the networkhierarchy. A wide-area network (WAN) may be provided to connect theintermediate level to the higher level. This configuration, whichdistributes the ‘network intelligence’ among many data collection nodes,serves the purpose of reducing the data flow into the central databasewhen a large number of meters are analyzed for load profile or intervalconsumption data. It also serves the purpose of reducing air-messagetraffic between the intermediate node and the higher-level concentratornode. However, this configuration becomes inefficient in the common casewhere only a part, or even none, of the meter population requiresadvanced metering services like time-of-use (TOU) rates, while basicdaily metering service is required for the whole meter population. Thisinefficiency is imposed by the short-range radio link between the metersand the data collection nodes, which significantly limits the number ofmeters a node can serve, regardless of how many meters need to be readfrequently for interval consumption data. In this case, an expensiveinfrastructure of up to thousands of data collection nodes may bedeployed, which often results in a great deal of unused excess capacity.A more efficient network would therefore be desirable, in order toreduce basic equipment cost, as well as to reduce installation andongoing maintenance costs.

Another inefficiency arises due to the fact that with a large number ofdata collection nodes, the most cost-efficient wide area network (WAN)layer in these multi-tier networks would be a wireless WAN. However, toavoid interference from meter modules, as well as to avoidover-complication of the data protocols, an additional, licensedfrequency channel is typically used for the WAN, adding to the overallcost of services to the network operator. A network composed of only onewireless data collection layer would therefore be desirable,particularly if operating in the unlicensed Industrial, Scientific andMedical (ISM) band.

Yet another disadvantage of networks with distributed intelligence amongdata collection nodes is the limited storage and processing power ofthese nodes. A system that could efficiently transfer all the raw datafrom the meter modules to the network's central database would thereforebe desirable, since it would allow for more backup and archiving optionsand also for more complex function calculations on the raw meter data.

Another prior data collection network includes only a few receptionsites, each one capable of handling up to tens of thousands of meters.In order to obtain long communication range, meter module antennas mustbe installed in a separate (higher and/or out of building) location fromthe meter module, and wiring must be added between the meter module andthe antenna, creating significant additional cost to the meter moduleinstallation, and significantly reducing the commercial feasibility forpractical deployment of the network.

None of the above-mentioned systems of the prior art offers a level offlexibility that will enable a network operator to deploy a reliable,low cost, fixed data collection network, which will meet a wide range ofAMR application requirements, from basic daily meter reads to fulltwo-way capabilities. Inefficiencies exist in the prior two-waynetworks, in which the two-way capability is imposed on the entire meterpopulation, and also in the prior one-way networks, in which small cellconfiguration requires a large, unnecessary investment ininfrastructure.

It is therefore desirable to introduce a simple to deploy, but highlyscalable, modular, and reliable data collection system, which wouldoffer a wide range of service options, from basic metering, to advancedapplications based on interval consumption data, to full two-wayapplications, while keeping the system's deployment and ongoing costsproportional to the service options and capacity requirements selectedfor various segments of the meter population.

SUMMARY OF THE INVENTION

According to a preferred embodiment of the present invention, a one-waydirect sequence spread spectrum (DSSS) communications network,implementation of which is well-known in the art, is used as the datacollection channel (uplink) of an automatic meter reading (AMR)application, and an optional paging network, or other suitable forward(downlink) network, may be used in a cost-effective manner. Theinvention provides a wide-area data collection network which is capableof supporting as many meters on as large a geographical area as requiredby the associated metering application.

The communications network may include one-way meter modules(transmitters) each communicatively coupled to a corresponding electric,gas or water utility meter, and may include two-way meter modules(transceivers) each coupled to such a corresponding utility meter. Themeter modules are simple to install, and are typically installed insideelectric meters, are integrated (as between meter and index) in gasmeters, or are provided as external units adjacent to water meters. Themeter modules monitor, store, encode and periodically transmit meteringdata via radio signals (air messages) in an appropriate RF channel,typically within the 902-928 MHz Industrial, Scientific and Medical(ISM) band, allocated by the Federal Communications Commission (FCC) forunlicensed operation.

Metering data air messages are collected by a network of receiver BaseStations (BS), decoded and forwarded to a central location, referred toas a Data w Operations Center (DOC), via a communication backbone suchas a frame relay network. The DOC communicates with all the basestations, monitors their operation and collects metering data messagesfrom them. The DOC may also be communicatively coupled to a pagingnetwork, or other wireless network, for sending downlink commands to thetwo-way meter modules in the network. By using appropriate designparameters of a DSSS signal transmitted by a meter module, air messagescan be received at a range of over 5 miles in urban areas, allowingsparse infrastructure deployment for a wide variety of metering datacollection applications.

By applying long range DSSS to AMR applications, a new level offunctional flexibility and network efficiency may be obtained. Thesegoals are additionally achieved by a low-cost, energy efficient metermodule which provides significant benefits to the system, primarily bycontributing to the long range of the wireless link by implementing adirect sequence spread spectrum (DSSS) signal transmitter of high outputpower and high interference rejection, while consuming very low averagepower, thus enabling long life (many years) battery operation.

One of the primary advantages of the invention is that it permits use ofa long wireless communication link, which provides wide-area coveragewith a small number of sites (typically tens of thousands of meters in afive-mile radius per base station), thereby simplifying networkdeployment, reducing infrastructure initial and ongoing costs, andreducing the number of potential failure points in the network toincrease reliability.

Another advantage of the invention is the provision of a modular networkarchitecture, enabling flexibility in network planning in order tooptimize cost and capacity in various regions covered by the network. Apart of the network's modularity is that a forward (downlink) channel,such as a paging network, can be integrated with the data collection(uplink) channel, providing a convenient transition to supplying dataservices to both one-way and two-way meter modules.

Still another advantage is the scalability of the network, which enablesgradual and cost-efficient increase of infrastructure deployment inorder to meet a wide range of application and capacity requirements,including requirements relating to interval consumption dataapplications. Another advantage is the routing of all raw metering datato the DOC central database, where it can be easily processed, archivedand accessed.

Briefly, the invention, in its preferred embodiments, is a scalable andmodular fixed-base wireless network system for wide-area metering datacollection, composed of at least one of each of a meter module, areceiver base station, and a data operations center. The system in itsbasic form includes one-way uplink meter modules, but may be scaled upin its air message handling capacity and in its application features byintegrating two way meters responsive to a wireless data-forwarding(downlink) channel, thus providing the system operator with considerableflexibility in the choice of network capacity, features and system cost.

The network components of the system of the invention include one-way(transmit only) and two-way (transmit and receive) meter modules, whichmonitor, store, encode and periodically transmit metering data via radiosignals (air messages). Also included are receiver base stations, whichreceive, decode, store and forward metering data to a central databaseand metering data gateway, referred to as the Data Operations Center(DOC). Base stations do not perform any meter data processing, butsimply transfer decoded air messages to the DOC. The data operationscenter communicates with all of the network's base stations and receivesdecoded air messages from the base stations. The DOC processes,validates and stores metering data in a meter database that it maintainsfor the entire meter population operating in the network and has thecapability to export or forward metering data to other systems viastandard data protocols.

An optional wireless downlink channel, such as a paging network, may beutilized to provide two-way service to two-way meter modules that may beoperating in the network. This downlink channel enables timesynchronization and other commands to be sent to two-way meter modules.

The system of the invention permits optimal adjustment of networkcontrol parameters such as the quantity of base stations, the number ofreception frequency channels, and the meter module message bit rate,according to application requirements such as message deliveryprobability, metering data latency and meter module battery life. Thesystem may also include Network Transceiver/Relay (NTR) devices,designed to enhance network coverage in areas of poor or no initialcoverage. The NTR devices retransmit messages only from designated metermodules, identified either by module identification number or by anappropriate flag in the meter module air message.

In one embodiment, the system utilizes a logarithmic table encodingmethod for compressing interval consumption data air messages to reducethe number of bits required in a message for each consumption interval.In this method, the DOC maintains a large list (bank) of consumptionencoding/decoding tables, adapted to various consumption patterns. TheDOC further maintains a registry specifying which set ofencoding/decoding tables is assigned to each meter module with the setsof tables potentially differing from one meter module to another. Alsoavailable is an interleaving encoding method for interval consumptiondata air messages, to increase the redundancy level of the data and/orto provide data for smaller consumption intervals. In this method, thetime base for each interval consumption data message is shifted,compared to the previous message, in a cyclic manner, so that intervalconsumption data may be reconstructed even if some of the messages arenot received.

The invention provides a low-cost, high-output-power meter module, whichmay operate in the system described above. The module includes a sensor,data storage and processing, a direct sequence spread spectrumtransmitter which may have an output of between 0.5 and 1.0 watt, and anantenna, all within the same physical enclosure.

The meter module preferably is equipped with a power supply in which acapacitive element and a limited current source are combined, in orderto allow high output power during a short transmission burst, which mayalso be initiated immediately in the event of a power outage. Thecapacitive element and the limited current source impose a physicallimitation on the charge time and thus the transmission duty cycle toreduce interference that can be caused by a malfunctioning meter moduleto an acceptable level that does not affect network functionality.

The meter module maintains low power consumption in its meter interfacecircuitry, and low overall power consumption, by using two sensors todetect rotation in the meter being monitored. These two sensors areopenable and closeable switches, of which only one (or neither) may havea closed switch status at any given time, with the switches beingoperated by the operation of the meter, as by rotation of a disk, forexample. Each switch is connected to a sensor circuit, and by disablinga sensor circuit as soon as a closed switch state is detected, whilesimultaneously enabling the other sensor circuit, near zero current isdrawn by the sensors.

The meter module also includes an outage recovery system, which providesimmediate notification of outage (‘last gasp’), immediate notificationof power restoration, and storage of interval consumption data prior toan outage event, thereby enabling a transmission of the last saved datashortly after power restoration.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing, and additional objects, features and advantages of thepresent invention will be understood by those of skill in the art fromthe following detailed description of preferred embodiments thereof,taken with reference to the accompanying drawings, wherein:

FIG. 1 is a block diagram illustrating required and optional componentsof a data collection network system according to an embodiment of thepresent invention;

FIG. 2A is a block diagram illustrating a two-way meter module inaccordance with the present invention;

FIG. 2B is a block diagram illustrating a one-way meter module inaccordance with the present invention;

FIGS. 3A and 3B are graphic illustrations of consumption data requiredto be transmitted in an air message;

FIG. 4 illustrates in tabular form examples of encoded logarithmicconsumption data;

FIGS. 5A-5D graphically demonstrate the evaluation process by which ameter module determines which consumption data-encoding table to select;

FIG. 6 is a flowchart of the process of generating logarithmic encodedinterval consumption data;

FIG. 7 illustrates the message contents;

FIG. 8 is a flowchart of the process of decoding the transmittedmessage;

FIGS. 9A, 9B and 9C illustrate interleaving encoding, which is used togenerate interval consumption data air messages;

FIG. 10 is a flowchart illustrating the process for generatingconsumption data messages without consumption data interleaving;

FIG. 11 is a flowchart illustrating the process of generating andhandling interleaving encoded interval consumption data messages;

FIGS. 12, 13 and 14 are flowcharts of consumption data recovery in theevent of power outage;

FIG. 15 is a block diagram of a first embodiment f the meter module ofthe invention;

FIG. 16 is a block diagram of a second embodiment of the meter module ofthe invention;

FIG. 17 illustrates a prior art ‘zero current’ rotation sensor;

FIG. 18 illustrates a zero current rotation sensor in accordance withthe present invention;

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT

Data Collection Network

Turning now to a more detailed description of the invention, FIG. 1illustrates a scalable and modular wireless fixed-base data collectionsystem, or network 10, comprising at least one wireless meter module,such as a two-way (transceiver) module 12, at least one receiver site(base station) 14, and one central site (data operations center) 16,into which all metering data is collected. According to a preferredembodiment of the present invention, system 10 is an automatic meterreading (AMR) system which uses a one-way direct sequence spreadspectrum (DSSS) communications network as a data collection channel(uplink) 18. A downlink network 20, which may be a paging system orother suitable downlink network, provides an optional forward (downlink)channel 21 in a cost-effective manner. The network 10 is designed toprovide a cost-effective, wide-area data collection solution which iscapable of supporting as many meters in as large a geographical area asmay be required by the associated metering application.

The communications system 10 may include one or more one-way metermodules (transmitters) 22 communicatively coupled, for example, tocorresponding electric, gas or water utility meters, and may alsoinclude one or more two-way meter modules (transceivers), exemplified bymodule 12, coupled to such utility meters. The meter modules 12 and 22monitor, store, encode and periodically transmit metering data via radiosignals (air messages), in an appropriate RF channel, such as thechannel 18. This RF channel is typically within the 902-928 MHzIndustrial, Scientific and Medical (ISM) band, allocated by the FederalCommunications Commission (FCC) for unlicensed operation. Metering datamessages are collected by a network of receiver base stations 14.

By using appropriate design parameters for a DSSS signal transmitted bymeter modules 12 and 22, air messages can be received at the remote basestations 14. In a preferred embodiment, a signal of 1 Watt of outputpower, a raw data bit rate of 4000 bits per second, a high antennaefficiency (near 1) and a processing gain of 24 dB are used. Inaddition, appropriate error correction methods, as known in the art, areincorporated; for example, a convolution code with R value of ½ and Kvalue of 5, combined with a data interleaving mechanism may be used. Thereception range can then be estimated by using empiric models such asthe Okumura model, which represents path losses in an urban environment,yielding an expected reception range of over 5 miles in urban areas,allowing sparse infrastructure deployment for a wide variety of meteringdata collection applications. The Data Operations Center (DOC) 16communicates with all the Base Stations (BS), monitors their operationand collects metering data messages from them. The DOC 16 may becommunicatively coupled to two-way modules in the network 10 by way ofdownlink network 20, which preferably is a paging network, a cellularnetwork, or other wireless network, for sending downlink commands to thetwo-way meter modules using suitable, wireless data protocols.

Since transceiver power consumption is greater than transmitter powerconsumption, it is generally preferable to use transmitters where thepower source is limited. Gas and water meter modules generally have alimited power source, typically from a battery, so the meter modulesattached to such meters are generally transmitters rather thantransceivers. Electric meters can typically take their power from theelectric grid, so their power is not limited, and hence transceivers aresuitable for electric meters. However, because the cost of thetransceiver meter module is greater than the cost of the transmittermeter module, electric meters may use a transmitter to save on the endunit cost. Thus, it is preferred that gas and water meters usetransmitters only, while electric meters may use transmitters ortransceivers according to the application requirements. The transceiverscreate a two-way system, which has the advantage of greater capacitythan a one-way system, and which can provide additional services (suchas remote connect or disconnect, over-the-air programming orreprogramming of meter module parameters, and others) that cannot beprovided by a one-way system. The metering data collection systemoperates as a one-way data collection system if not coupled to adownlink channel. The basic one-way network may be scaled up to severalhigher levels of capacity and application features, as described herein,the highest level being reached by integrating a downlink channel in thesystem.

The system 10 thus comprises both one-way (transmitter) meter modules 22and two-way (transceiver) meter modules 12 coupled to correspondingmeters. All of the modules are able to transmit encoded DSSS radiosignals representing metering data stored in the meter modules, such ascurrent meter reading, tamper status, meter identification data andinterval consumption data. A variety of utility meter module types(electric, gas, water) and models may operate in one metering datacollection network, utilizing the module, base station and dataoperations center infrastructure. Each receiver base station 14 is ableto receive and decode DSSS encoded signals (air messages) generated byany of the meter modules 12 or 22. The bandwidth of the DSSS signal isapproximately 2 MHz, and the base stations are preferably optimized toreceive signals in any radio frequency range between 800 MHz and 1 Ghz.In a preferred embodiment, the data collection network operates in theISM band under the rules for unlicensed operation (Part 15 of the FCCRules), and requires no licensing for any portion of its wireless uplinkchannel 18.

According to the preferred embodiment, one or more base stations 14 aredeployed to cover a geographic area. The number of base stations neededdepends on the size and type of terrain within the geographic coveragearea, as well as upon application requirements. A base station istypically installed at a high location (communication tower or roof top)and consists of at least one receiving antenna, RF cables andconnectors, a DSSS receiver, and a communication interface such as a PPProuter or CDPD modem. A base station may also contain a backup powersource for continued operation during a specified period of outage. Basestations 14 receive metering data air messages from meter modules 12 and22 on the uplink channel 18, decode the radio signals, and relay thedecoded metering data air messages to the DOC 16. The DOC preferably iscoupled to the base stations 14 via standard communication channels 24,which typically may be using an IP network (such as frame relay orInternet). Other communication channels may be used between the DOC andthe base stations, and such channels may be a wireless cellular network,CDPD, PSTN or a satellite data network.

The DOC 16 preferably includes, or has access to, a database 25 of allthe meter modules 12 and 22 in the network 10, and an Internet serverenabling remote access to the database. This embodiment also may includeemail, fax, pager devices or voice message generators in the DOC 16 toprovide alerts and event notification to the network users. The DOC 16may be programmed to forward received data directly to a user or toexport files to a buffer directory by using standard data protocols.

According to the preferred embodiment, the DOC 16 includes suitableprograms for metering data validation, processing and storage, while therole of the base stations 14 is to decode air messages and forward rawmetering data to the DOC for central processing. This network structureeliminates the need to monitor and control metering data processingtasks, which are carried out in multiple locations; instead, allmetering data is stored in a central location, enabling fast data accessresponse times. Further, the central location (DOC) is equipped withsuitable backup storage means to provide a permanent record of allreceived data. Thus, two objectives are served: low initial andmaintenance cost of base station hardware and software; and convenient,permanent access to all metering data collected by the network via onecentral data repository.

The basic architecture of the network includes transmitter meter modules22, base stations 14 and a DOC 16. However, the network is modular andmay include a downlink network 20 and two-way meter modules 12, as wellas message relaying devices 30 in the uplink (reverse) RF channel 18. Inaddition, as will be further described, the network 10 includes avariety of scalability mechanisms enabling cost-effective service invarying levels of network air-message traffic and various metering dataapplications.

According to a particular embodiment of the invention, a cost-efficientmeans for expanding network coverage is the addition of a NetworkTransceiver/Relay device (NTR) 30, for example in one or more of thechannels 18 to provide coverage for meter modules experiencing poor orno base station coverage. This provides more flexibility to the networkoperator by creating another option for providing coverage to a limitedgeographic area. The cost of deployment and maintenance of an NTR issignificantly lower than that of a base station so that, besides being acost effective solution to poor coverage, it also may justify theenhancement of a network's coverage to areas of low population density,thus extending the reach of the automated metering data collectionsystem. The deployment of NTR devices does not require the networkoperator to perform any changes in any of the other elements of thenetwork infrastructure.

In the design of the system 10, an analysis of expected radio trafficmay indicate sufficiently high radio traffic to cost-justify full basestation coverage. However, in any network it is likely that there willbe certain areas, or “holes”, in which radio traffic will be very sparseand which cannot cost-justify Base Station coverage. NTRs may then beused to provide sufficient coverage at much lower cost. For example, asmall number of meters might be located in a deep valley, and so mightnot be covered by the nearest base station, but the deployment of a newbase station might not be economically justified. In this case, an NTR,which only needs to provide limited coverage and thus is smaller in sizethan a base station, may be mounted at a common site such as on a poletop, so that its ongoing site lease cost would be significantly lowerthan that which an additional base station would require. The use of aNTR is thus a low-cost means of covering holes in the coverage of thebase station network, or of extending the network's coverage to areas oflow air-message traffic.

The network transceiver/relay device 30 illustrated in FIG. 1 mayreceive metering data messages from one or more meter modules 12 and 22,and operates to. decode and retransmit messages from specific metermodules. NTR devices 30 are used in specific terrains that endure poorradio coverage, as described above, or may be used to remedy othersituations where there is a lack of coverage or where coveragedegradation occurs. The NTR 30 preferably is a low cost data relay node,which includes a DSSS receiver that may have lower RF sensitivity andsmaller coverage (hundreds of meters) than a base station, and that alsoincludes a DSSS transmitter. Like the base station, the NTR does notperform any metering data analysis; it only receives, encodes andretransmits raw data air messages that are identified as coming fromspecified meter modules listed in the NTR's memory. The relayed messagesmay then be received by a nearby base station 14.

In another embodiment, the NTR 30 may include a program which checks foran NTR flag bit in a received air message that indicates whether or notto relay the message. If desired, this embodiment may be combined withthe above-described embodiment in which the NTR 30 only receives airmessages from listed meter modules to allow selection of specific metermodules which will have their air messages retransmitted, with eachmeter module being programmed to use its NTR flag in order to have onlysome of its air messages retransmitted. This enhances network coverage,without creating unnecessary air message traffic.

One embodiment of a two-way meter module, such as that indicated at 12in FIG. 1, is illustrated in the block diagram of FIG. 2A. This moduleis capable of transmitting metering data air messages on demand; forexample, upon receiving an appropriate downlink wireless command.Alternatively, or in addition, the module may also be convenientlyprogrammed to transmit at specific times by incorporating andmaintaining a real-time clock which may be synchronized, for example, bya suitable signal transmitted in the wireless downlink channel 21.Two-way meter modules preferably also receive, decode and execute othercommands such as commands to program meter parameters, to displaymessages or alerts on the meter's display, and to disconnect andreconnect power to the utility meter's load.

As illustrated in FIG.2A, the two-way module 12 incorporates a receiver40 connected by way of inlet line 42 to an antenna 44, and a transmitter46 connected by way of outlet line 48 to an antenna 50. The receiver 40may be a pager receiver, for example, and includes an output line 52connected to a POCSAG/Flex Decoder 54 which receives and decodesdownlink wireless command signals for controlling the module. Onedecoder output line 56 leads to a meter 58, which may be a utility meteror the like as discussed above, to provide command signals to the meter,while a second decoder output line 60 leads to the transmitter 46 tocontrol its operation; for example, to turn it on and off at selectedtimes. The meter 58 is connected to the transmitter 46 by way of meteroutput line 62, to supply data which is to be transmitted.

FIG. 2B is a block diagram of a one-way meter module 22, which includesa transmitter such as the transmitter 46 of the module 12, connected toantenna 50 by way of line 48 and to meter 58 by way of line 62. Thetransmitter in this module is controlled by an internal clock to operateperiodically to transmit data from the meter 58. The basic transmitterapparatus will be described below. A trade-off exists between the amountof data required by a particular use of the system and the maximumnumber of air message transmissions that can be accommodated while stillmaintaining air message traffic or meter module battery life atacceptable levels. In the preferred embodiment, the system is designedso that the network operator or deployment planner has the flexibilityto optimize space diversity, frequency diversity and air messageduration according to the various requirements of delivered meteringdata, meter module battery life, metering data latency, and air messagedelivery probability.

To meet these various requirements, five different levels of networkcapacity control may be provided by the system, depending upon customerdemand, it being noted that levels 2 to 5 described below may beimplemented in any order. The most basic system capacity may be definedas Level 1, wherein a sparse base station network is deployed, combined,if necessary, with NTR devices which would cover areas with very limitedradio traffic. This level, which provides adequate geographic coverageand a minimum level of system capacity, is roughly defined as thenetwork capacity required in order to provide daily readings of metersin an urban meter population. A typical urban deployment for this levelwould include base stations spaced 5 miles apart, each covering up toseveral tens of thousands of meters, with few to no deployments of NTRdevices. As an example, a basic configuration may utilize one RFchannel, and provide daily coverage for 99% of an area, in which 50,000meters are deployed and are transmitting daily, the area being coveredby five Base Stations. Additional capacity requirements may be triggeredby significant growth in the meter module installed base and/or by newapplications requiring more data to be delivered daily from each metermodule. In order to maintain a desired level of data collectionservices, one of the four measures described below may be used.

To obtain a higher, Level 2, system capacity, a space diversitytechnique is used. In this arrangement, the number of base stations isselected to provide coverage for a specified meter population and aspecified metering data application in a specified geographical area. Inthe initial phase of planning, the system coverage for this levelincludes selection of the optimal number and locations of base stationsto be deployed in the specified area. However, when a base stationcovers a large area and the meter module density or air messagefrequency requirements increase above the initial design coverage, atsome stage the farthest meter modules encounter interference from thecloser meter modules, and message reception probability from thefarthest meter modules decreases. To overcome this problem, basestations may be added at appropriate locations in the same geographicarea, thereby increasing network capacity and message reception rate.Adding base stations reduces the effective range between each deployedmeter module and the base station closest to it, so that more metermodules, or potential meter module locations, are within a range of highair-message reception probability. Thus, the placement of additionalbase stations in the same geographic area, without any other change inthe network or the meter modules, will in itself increase overallnetwork capacity.

Another approach to increasing network capacity, defined as Level 3,utilizes frequency diversity, which is implemented by utilizing morethan one frequency for uplink channels within a given coverage area. Theuplink channels 18 would normally operate on the same radio frequency,but selected meter modules may be programmed to alter their transmissionfrequency channel; for example, to transmit each successive air messageon a different frequency. To accommodate this, the corresponding basestation would include several receivers each tuned to a differentfrequency, or a single receiver having multiple frequency channels, thussignificantly increasing the base station's air message receptioncapacity. Frequency diversity may eliminate or at least postponecoverage problems, which would otherwise require adding base stationsites. In addition, frequency diversity may be combined with spacediversity by feeding receivers operating in different uplink frequencychannels at the same base stations with signals from separate antennas.In the 902-928 MHz unlicensed ISM band, a particular embodiment of thenetwork may operate in up to 57 channels, spaced 400 kHz apart, but amore practical limit for reliable operation would be about 10 channels.Each new frequency channel added to a receiver increases the basestation's capacity, and when a regional base station network is beingused, adding channels significantly increases the entire network'scapacity.

Still another approach to increasing system capacity, defined as Level 4and which may be included in the preferred embodiment of the system,consists of modifying the length of the direct sequence code used toencode the command and data signals in the network, although this formsa trade-off with the air message's raw data bit rate parameter. In oneembodiment of the invention, for example, the direct sequence chip ratefor the code may be 1 Mchips/sec with a maximum code length of 255chips, yielding a data rate of about 4 kbps. To modify this, the networkoperator/planner may select shorter codes, namely 63, 31 or 15 chipslong, thus increasing the raw data bit rate. Reducing code lengthreduces the signal spreading and decreases the coverage range per basestation, but on the other hand increases each base station's air messagecapacity because of the shortened air messages.

The highest level of air-message capacity, which may be defined as Level5, can be attained in a data collection network by utilizing a downlinkchannel and two-way transceivers rather than one-way transmitter metermodules. A two-way system has the inherent potential to be moreefficient with radio air time resources, since field units may besynchronized to a central clock to allow transmission only in allocatedtime slots. The higher the number of two-way meter modules in a meteredpopulation, the higher is the network capacity increase provided byadding the downlink channel. A wireless data collection network in whichthe modules incorporate transceivers as described above may be scaled upfrom one-way (data collection only) to two-way, simply by connecting theDOC 16 to a wireless downlink channel 20. The measures described inlevels 2 to 4 above may be implemented in such a two-way network aswell, in order to further increase network capacity.

Integrating a downlink channel such as channel 20 is a cost-efficientscaling-up procedure, which provides significant enhancement of bothnetwork air-message capacity and metering data applicationfunctionality. This enhancement does not require the network operator toperform any changes in any of the already existing elements of thenetwork infrastructure, if the modules already contain tranceivers.

In a preferred embodiment of a two-way metering data system 10, bothone-way (transmitter) and two-way (transceiver) meter modules areutilized. Transceivers can be interrogated for data at the time that thedata is required, thus eliminating the need for the retransmittedtransmissions which are required in a one-way network in order tomaintain a certain level of data latency. In addition, by synchronizingall transceiver modules to one central real-time clock, a time slot fortransmission may be allocated and specified for each transceiver in acoverage area, thereby increasing the efficiency of network air timeusage. Although several advanced metering applications, such as demandand Time of Use (TOU) metering, are available from a one-way meteringdata collection network, two-way meter modules operating in thedescribed two-way metering data network are capable of providingadditional features, such as accurate interval consumption datameasurement enabled by a regularly synchronized real-time clock,on-demand meter reading, remote disconnect and reconnect, remoteprogramming of meter parameters, and remote notification of rate changesor other messages. The particular embodiment of the data system of thepresent invention enables the operator to mix on the same network, in acost efficient manner, low cost transmitters, which provide a wide rangeof metering data collection features, and higher cost transceivers,which further enhance metering data application features, whilemaintaining the core advantages of sparse infrastructure and the lowcost associated with unlicensed operation of the metering datacollection branch of the network.

In addition to the scalability and flexibility provided by the levels ofnetwork architecture described above, another key feature of the systemis application scalability, which is a cost-efficient method ofenhancing the metering applications supported on the network. Asdescribed above, some application features, including on-demand meterreading, remote disconnect and reconnect, remote programming of meterparameters and remote notification of rate changes or other messages,require that the network architecture be scaled up to a two-way networkby adding a downlink channel. However, some applications based oninterval consumption data, such as demand analysis, load profiling, andtime of use rates, can operate successfully on a one-way network and, byusing the method described hereinbelow, only a relatively minor increasein air message traffic occurs.

Consumption Data Encoding Methods

In the prior art, extensive infrastructure is deployed in order tocollect interval consumption data frequently (e.g. every 15 minutes).However, in many cases, particularly in residential meteringapplications, consumption data may be required in high resolution, butsome latency is permitted in data availability. For example,fifteen-minute demand analysis could be required, but may be performedeach morning on data collected the previous night, allowing severalhours in which to collect the required interval consumption data. Itwould, therefore, be beneficial for the network service provider to havethe flexibility to deploy infrastructure appropriate to the applicationand invest in additional infrastructure for high-end applications, suchas on-demand reads, only in proportion to the meter population for whichit is required.

Such interval consumption data measurements may be obtained from ameter, in accordance with one embodiment of the invention. Such ameasurement normally includes an array of interval consumption values,each one of the values representing the consumption increment of oneinterval. The meter module transmits a regular (‘full data’) message,that contains the exact absolute reading of the meter several times aday, and in addition transmits several messages daily (‘interval datamessages’) that include the interval consumption data array and areference reading (e.g. the least significant two digits of the meterreading). As a one-way system, the data collection network does not relyon a real time clock in the meter module, but rather uses a time stampgenerated by the DOC. Therefore, the following method is used forgenerating interval consumption data at the DOC: when an interval datamessage is received, the DOC traces the most recently received full datamessage and ‘completes’ the most significant bits of the meter readingat the time of the interval data message. Then, using the incrementvalues received in the interval data message, an absolute meter readingcan be generated for all the intervals included in the interval datamessage. The result is an increasing function representing the meterreading at each interval, which is stored at the DOC.

In order to reduce the total length of air messages, or the total numberof fixed-length interval data air messages transmitted by a metermodule, a method referred to as “logarithmic table encoding” ofconsumption values is used, which encodes interval consumption data inthe air message. This method maps the range of consumption values into amore limited number of values, for the purpose of reducing the number ofbits of information transmitted over the air, with the mapping beingexecuted by a series of tables, which are predefined according to theexpected dynamic range of interval consumption values.

The charts 70 and 72 illustrated in FIGS. 3A and 3B are respectiveexamples of aggregate and interval consumption versus time data that maybe required by a demand analysis application. In this example, it isassumed that an accuracy of 0.1 kWh is sufficient. Also by way ofexample, consumption is measured over a 12 hour total time period during15 minute intervals. In order to optimize a consumption profile, thistotal time period may be divided into several sub-periods; in thisexample, 3 periods of 4 hours each. A table showing numeric measuredvalues for each interval is illustrated in FIG. 3B. In prior meterreading systems, these values would be encoded for transmittal, and thiswould traditionally require an encoding table with values ranging fromzero to 1800 Wh, in 100 Wh increments, i.e. 19 values, requiring 5 bitsper each consumption interval to encode.

In the present invention, the overall air message traffic associatedwith interval consumption data applications is reduced by using, in thisexample, only 2 bits for interval consumption encoding. This encodingrequires some approximation, which inevitably creates an error in thereconstruction of a consumption profile compared to the actualconsumption, but by appropriate definition of a set of encoding tablesfor the meter module to use, an acceptable error level may be reached.Flexibility in assigning different encoding tables for differentsub-periods also reduces the statistical errors in the decodedconsumption profile.

The set of tables assigned to a meter module may differ from one metermodule to another, according to the expected consumption patterns. TheDOC maintains a bank of available tables from which a set of tables isdefined for each meter module during installation. An example of such aset of encoding tables is shown in FIG. 4.

The meter module selects an encoding table from its assigned set oftables by building a consumption profile with each of the tables storedin its memory, and comparing it to the actual profile (FIG. 3A), storedin its memory as the aggregate of a series of actual interval readingvalues (FIG. 3B). Then the meter module applies a criterion by which toselect the best encoding table; e.g. the table that yields the lowestmaximum error during the metered period, or the lowest variance betweenthe encoded and actual profiles.

The encoded consumption profile is built in the following process: ifduring an interval, actual (aggregated) consumption reaches a value X,the interval consumption value which would bring the encoded consumptionprofile to the closest value less than or equal to X, and which is alsorepresented by a two-bit code in the encoding table, is used in order tobuild the encoded consumption profile. Examples of constructed profilesvs actual consumption for Tables 1-4 of FIG. 4 are shown in FIGS. 5A-5D,respectively. In the examples, if a minimum error criterion is appliedfor the 6-10 four-hour period shown, then Table 3 would be chosen fortransmission, as it yields a maximum error of 200 Wh (0.2 kWh) duringthe period. A table is selected for transmission for the other twoperiods in the example of FIG. 3B (10-14, 14-18) in an identicalprocess. A reverse process is applied at the DOC in order to extract theinterval consumption data. Thus, the table set used by the meter moduleis retrieved and then the consumption profile is reconstructed for eachsub-period.

A summary of the logarithmic encoding and decoding process is shown inFIG. 6, where, for each sub-period P1, P2, P3, interval consumptionvalues are calculated using each of the available four tablesT1,T2,T3,T4 as illustrated at blocks 80, 82 and 84. After eachcalculation, a criterion is applied for each period to select the mostsuitable table for encoding the interval consumption of that period, asillustrated at blocks 86, 87, 88, 89; and 90, 91. Two bits that identifythe table that was used for each period are also attached to the airmessage (total of 6 bits in the example), and the message istransmitted, at block 92. The transmitted message is illustrated in FIG.7 as including a message header 94 which includes the identification(ID) of the meter module which has calculated the data, and thenincludes the data itself, as indicated at 96.

As illustrated in block 98 of FIG. 8, when the DOC receives the messagefrom a meter module, it identifies the type of message and the ID of thetransmitting module, as indicated at block 100. The DOC then determinesthe tables to which the table identifiers in the message refer (block102), and once the tables are identified, the DOC decodes the intervaldata encoded in the message into actual consumption (Wh) values (block104).

As illustrated in FIG. 7, an interval consumption air message in theprovided example may contain 2-bit interval data for 48 intervals of 15minutes; i.e. 96 bits, plus two bits identifying the table chosen foreach of the three sub-periods, plus 10 bits as a reference meter read,plus a message header of 40 bits, for a total of 152 bits, compared to 5bits×48 intervals, which would amount to 240 bits and a total of 290bits including the header, in a traditional system with no logarithmicencoding. Thus, airtime usage or the number of required messages isreduced by about 47% using the described method.

In order to provide a high level of redundancy of interval consumptiondata, another data encoding method is provided, referred to as intervalconsumption data “interleaving air message encoding”, which splitsinterval consumption values between separate messages. In a particularembodiment, depicted graphically in FIGS. 9A-9C, and in FIG. 11, threeseparate interval consumption data air messages 130, 132 and 134, aretransmitted that relate to the same consumption period b-a. The firstair message includes samples taken at times a, a+x, a+2x, . . . and istransmitted at time b. The second air message includes samples taken attimes a+x/3, a+4x/3, a+7x/3, . . . b+x/3, and is transmitted at timeb+x/3. The third air message includes samples taken at times a+2x/3,a+5x/3, a+8x/3,b+2x/3, and is transmitted at time b+2x/3, as illustratedat block 136 in FIG. 11. More generally, in order to spreadtransmissions during the day, the offset between interval data arraysmay be x/3+Nx, where N is an integer.

In a prior art interval consumption data handling method, described inFIG. 10, an interval consumption data array 116 is generated by fillingthe value C₁ with the incremental consumption of the current interval(block 114), and shifting down all of the array cell values at the endof each interval X (block 120). That way, after a metered period of nX,n values relating to the last n intervals are stored in the AMR module.Once the array is full it is ready for transmission (block 118 to block122). If, for example, a redundancy level of 3 is desired, it isobtained by sending each interval data message three times (block 122).Then the array is set to zero (block 110) and starts aggregating datafor the next interval data message.

In a particular embodiment, described in FIG. 11, the present systemprovides a redundancy level of 3, by storing three interval consumptionarrays (130, 132 and 134), while having their time base cyclicallyshifted by X/3 from each other (block 136). Per each array, the metermodule executes the same process described in FIG. 10 (block 138), withthe exception of needing to transmit the interval data message justonce. The redundancy is provided by having three interval data arrayscovering the same metered period, although not having the same intervalstart and end times within that metered period.

With interleaving encoding, internal consumption data is defined to havea resolution value corresponding to the size of the time intervalbetween consecutive consumption values sampled. If a message is lost,interval consumption data is still available at the DOC with aresolution of x or better. If no messages are lost, the DOC canreconstruct the absolute reading in x/3 intervals. i.e. with aresolution of x/3, illustrated at block 140. This way, the meter modulemaintains the potential to provide high resolution interval consumptiondata, but also provides lower resolution interval consumption data witha higher redundancy level than that available when data is not split asdescribed above, as illustrated at blocks 138 and 140.

Although each of the methods may be applied independently, by combiningthe two encoding methods described, a highly reliable and efficientinterval consumption data collection system is provided. In the exampleof FIGS. 3A and 3B, 8 daily messages, which include two regular meteringmessages (not containing interval data) and six interval data messages(each one 152 bits long, as in the example above) are required todeliver interval data, with a redundancy level of 3, whereas withoutusing the provided methods, and using a comparable message size of 150bits, two regular metering messages and twelve interval data messages,or a total of 14 daily messages, would be required to achieve the sameredundancy level. Therefore, the encoding methods provided by thepresent invention maintain high channel reliability while increasingnetwork capacity, by 75% in this example.

The system of the present invention supports interval consumption dataapplications even when a power outage occurs. This is performed byappropriate utilization of the meter module non-volatile memory, andwithout requiring any backup battery. A method, combined with themethods described above for data encoding, for retrieving intervalconsumption data in a one-way data collection network after an outageevent has occurred utilizes a meter module which periodically andfrequently executes a procedure to update and store interval consumptiondata messages,—as illustrated in FIG. 12. The purpose of this process isto prevent loss of interval consumption data upon the occurrence of anoutage event. The flowchart of the data recovery process related to anoutage shown in FIG. 12 is similar to that of FIG. 9, but furtherincludes storing consumption data in an EEPROM 142. If an outage occurs,the meter module uses its power supply (referred to below in the metermodule description) to generate a ‘last gasp’ message (block 144, FIG.13) that indicates to the DOC (block 146 in FIG. 14) that power is outfor this meter module. Upon power restoration after outage (block 148),the meter module's microcontroller “wakes up”, and transmits a full datamessage which includes usual identification information, the readingfrom the EEPROM and also includes a flag signifying that power has justbeen restored as illustrated at block 146. At the same time, a newinterval consumption data cycle (period) begins, and shortly thereafterthe last saved three interval data message (arrays C₁₁-C_(1n),C₂₁-C_(2n), C₃₁-C_(3n)) are sent.

As illustrated in FIG. 14, block 150, after the DOC identifies the powerrestoration message flag, it receives the interval consumption messagesthat follow it as the last saved interval consumption messages, enablingthe DOC to reconstruct interval consumption data (block 152) prior tothe outage event. In addition, the next scheduled full data message,which follows the power restoration message is also flagged by the metermodule as the ‘second full data message since power restored’. This actsas a redundant measure to identify the last saved interval consumptionmessage before the outage event. In order to provide interval datarecovery after outage even in case the ‘last gasp’ message was notreceived, the time of outage can also be input to the DOC from othersystems (such as a utility customer information system).

Meter Module

The meter module apparatus used in the present system has uniquefeatures of low overall power consumption, high output power and lowcost overall design, enabling long battery life and long communicationrange in a commercially feasible fixed wireless network for a variety ofmetering applications. Each meter module in the network continuouslymonitors the resource consumption according to an input sensor that iscoupled to the utility meter. In a particular embodiment, the metermodule may be integrated inside, or as a part of, the meter enclosure,but in any case the meter module stores and transmits a wide array ofdata fields related to the meter, including consumption data, meteridentification and calculation factor data, and various status alerts.The meter readings are stored as an aggregated value and not asincremental values, thus maintaining the integrity of the meter readingif an air message is not received at the DOC.

A one-way meter module 22 (FIG. 2B) transmits a metering data airillustrated at block 146. At the same time, a new interval consumptiondata cycle (period) begins, and shortly thereafter the last saved threeinterval data message (arrays C₁₁C_(1n), C₂₁-C_(2n), C₃₁-C_(3n)) aresent.

As illustrated in FIG. 14, block 150, after the DOC identifies the powerrestoration message flag, it receives the interval consumption messagesthat follow it as the last saved interval consumption messages, enablingthe DOC to reconstruct interval consumption data (block 152) prior tothe outage event. In addition, the next scheduled full data message,which follows the power restoration message is also flagged by the metermodule as the ‘second full data message since power restored’. This actsas a redundant measure to identify the last saved interval consumptionmessage before the outage event. In order to provide interval datarecovery after outage even in case the ‘last gasp’ message was notreceived, the time of outage can also be input to the DOC from othersystems (such as a utility customer information system).

Meter Module

The meter module apparatus used in the present system has uniquefeatures of low overall power consumption, high output power and lowcost overall design, enabling long battery life and long communicationrange in a commercially feasible fixed wireless network for a variety ofmetering applications. Each meter module in the network continuouslymonitors the resource consumption according to an input sensor that iscoupled to the utility meter. In a particular embodiment, the metermodule may be integrated inside, or as a part of, the meter enclosure,but in any case the meter module stores and transmits a wide array ofdata fields related to the meter, including consumption data, meteridentification and calculation factor data, and various status alerts.The meter readings are stored as an aggregated value and not asincremental values, thus maintaining the integrity of the meter readingif an air message is not received at the DOC.

A one-way meter module 22 (FIG. 2B) transmits a metering data airmessage once every preprogrammed time interval, and a block diagram of afirst embodiment of the module is depicted in FIG. 15. In thisparticular implementation, the module includes a meter interface logicmodule 180 that collects consumption, tamper status and other data froman associated utility meter 58. It should be noted that although FIG. 15depicts a single meter interface module 180 for purposes ofsimplification, multiple meter interface logic modules may be used in asingle transmitter to interface with corresponding utility meters. Themeter interface logic module 180 operates continuously and draws only asmall amount of current. It includes several standard sensors (notshown), such as magnetic reed switches or optical sensors to trackconsumption, tilt sensors for tamper detection, and voltage sensors todetermine outage or power restoration events.

The module 22 also includes a controller module 182, which typically isa microprocessor, connected to the interface logic module 180 by way ofconnector 184 and connected to a serial data communication interface 186by way of conductor 188. The interface 186 includes a short-rangewireless magnetic loop output or other conventional personal computerdata port (not shown) connectable by way of input port 190 and conductor192 for testing and initialization of the transmitter at the shop or inthe field. The interface 186 is also connected by way of conductor 194to a wake-up circuit 196 which, in turn, is connected by way ofconnector 198 to the controller 182, by way of conductor 200 to themeter interface logic module 180, and by way of conductor 202 to a timercircuit 204.

A DC power supply 206 is connected to an internal (battery) or externalpower source 208 by way of conductor 210, with the DC power supply 211output being connected by way of conductor 212 to corresponding inputsfor interface 186, timer 204, wake-up circuit 196, and meter interface180. The wake-up circuit 196, when activated, connects the DC power online 112 to conductor 198, to thereby supply power to controller module182.

In the illustrated embodiment, the controller module 182 uses theauxiliary wake-up circuit 196 to manage a minimal power consumptionlevel during the times in which the meter module is inactive (“sleepmode”). Upon receipt of a command from the controller 182, the wake-upcircuit 196 operates an electronic switch to disconnect the power supplyfrom the controller itself, thereby also disconnecting the RFtransmitter module to be described, thus allowing very low overall powerconsumption of the meter module during a “sleep” period. The wake-upcircuit connects power back to the controller when triggered by anoutput from the meter 58 by way of interface 180, by an external deviceby way of the port 190 and interface 186, or by the timer 204. Thiscapability of the meter module is a particular value in battery-operatedtransmitters. However, it will be understood that if there is anunlimited power source, as may be the case if utility meter 58 is anelectric meter, the controller 182 may operate continuously, in whichcase the wake-up circuit 196 would not be needed, as illustrated in FIG.16. In this second embodiment of an electric meter module illustrated inFIG. 16, the timer 204 is a part of the controller module 182, and theDC power conductor 212 is connected directly to the controller module182, instead of being connected through the wake-up circuit.

The meter module 22 also includes a radio frequency (RF) module 220, aDSSS encoder 222, and a low pass filter (LPF) 224, connected to thepower supply output conductor 212 by way of the controller module 182and respective conductors 226, 228 and 230. The RF module 220 includes asynthesizer-controlled local oscillator (LO) 232 which is controlled bythe controller module 182 by way of conductor 234 to provide a carrieroutput signal on line 236 to an up-converter 238. The carrier signal ismodulated in converter 238, and the modulated output is supplied by wayof output conductor 240 to a power amplifier (PA) 242, the output ofwhich is fed by way of output conductor 244 to an antenna 246.

When the controller 182 determines that an air message is to betransmitted, it prepares a data packet, as described above, which issent to encoder 222 by way of conductor 250, where it is converted to adirect sequence through PN code generation and signal spreading. Thespread signal is supplied by way of line 252 to the low pass filter(LPF) 224 where it is filtered and sent by way of line 254 toup-converter 238 where it is used as the modulating base-band signal forthe signal to be transmitted. The power amplifier 242 produces up to 1 Wof power for output to antenna 246, which preferably is an on-boardprinted antenna. In the embodiment which utilizes the wake-up circuit196, once the controller 182 has handled the event that woke it up fromits power-down mode, whether an air message transmission or other taskwas performed, it returns to its power-down (idle) mode.

In a preferred embodiment of the meter module of the invention, thepower supply 206 is limited in order to maintain an acceptable level ofradio interference in the event of uncontrolled transmission by amalfunctioning meter module, for one source of danger in the system isthe possibility that a transmitter will malfunction and begintransmitting continuously. The result may be that the entire frequencychannel would be blocked in that coverage area during the time oftransmission, until the transmitter's power source dies. If the powersource is a battery, this would be a relatively short period, but theinterference would continue indefinitely if the power source isunlimited, such as would be the case if the meter is connected to anelectric grid. Although this event is highly unlikely, in the metermodule 22 described herein, a cost effective mechanism has beenintroduced to prevent uncontrolled transmission. This mechanism providestwo additional benefits to the system: high output power with a limitedpower source and an immediate outage notification feature, also known asa ‘last gasp’ transmission.

The meter module's power supply 206 includes two specific physicallimits to prevent continuous uncontrolled transmission; namely, acapacitive element 260 connected between output conductor 212 andground, and a limited current source. The capacitive element 260, whichis used as a buffer stage between the energy source 206 and the loadconnected to output line 212, stores sufficient energy to provide ahigh-power air message transmission, but due to its inherent physicallimitations, the capacitive element can deliver sufficient power fortransmission for only a limited period of time. Since the duration oftransmission is relative to the capacitance of element 260, andcapacitance is related to the size of the element, the size of thecapacitive element 260 is selected to be big enough to deliver enoughenergy for a complete transmission session, but not more than that. Thisway, the maximum potential blockage duration due to unwantedtransmission is restricted to one transmission session. In addition, thelimited current source in power supply 206 imposes a physical limitationon the recharge time required for the capacitive element to reach therequired energy level for another air message transmission, thuslimiting the on-off transmission duty cycle to a level that is harmlessin terms of network capacity.

In a particular embodiment of the invention, the transmitted power isone watt, for a duration of 150 msec, and the power supply provides arecharge time of 90 seconds. This translates into a maximum of 960messages per day, or 144 seconds a day, which is about 0.16% of theavailable time. Since network coverage is designed with a much highersafety margin, a malfunctioning transmitter would not be destructive tothe network operation, allowing sufficient time for detection andidentification of the source of the problem.

The described power supply enables the transmitter to generatehigh-power air message transmissions, even with a power source having avery low current drain. It also enhances electric metering applicationsby enabling a ‘last gasp’ metering data air message transmission when anoutage event is detected by an electric meter module, if the capacitiveelement is fully charged.

As an illustrative example of the design and power supply we assume thefollowing:

1. The transmission duration is 150 mSec.

2. The out put power is 1 Watt.

3. The power amplifier efficiency is 40% and its operation voltage is 5Volts.

4. Minimum time between transmissions −90 seconds.

The energy required for a single transmission is 1 Watt×0.15Sec/0.4=0.375 J. The energy stored in a capacitor is equal toE=0.5xCx(Vi^2-Vf^2) when C is the capacitor capacitance, Vi is theinitial voltage of the capacitor and Vf is the voltage which remains inthe capacitor after the completion of the transmission. Since the poweramplifier requires 5V regulated voltage, a reasonable voltage for Vf is8V. Selecting the capacitor's capacitance C and Vi can be done in morethan one way, so additional considerations can be made, such as theavailability of the selected capacitor in the market, its price, itssize etc. If, for example, the capacitance is selected to be 2200 uF,then in this case Vi is equal to 20V. Since the device that converts theenergy stored in the capacitor to a constant regulated 5V voltage tofeed the power amplifier (typically a step down regulator) has less than100% efficiency (typically 90%), Vi may be adjusted, taking into accountthe efficiency of the regulating device. A simplified charger can beimplemented as a simple current source. Since the minimum time betweentransmissions is 90 seconds, the current source should be able to chargethe capacitor from 8V to 20V in 90 seconds. Since 1=C×dV/dT, we get1=2200 uF×12/90=0.3 mA.

Conventionally, a utility meter such as meter 58 includes a rotatingsensor which responds to the utility being monitored; for example, anelectrical meter typically incorporates a rotating disk which respondsto utility usage to drive the meter indicators. The rotation of such adisk can be monitored by a suitable sensor such as a magnet or a lightsensor, for remote detection. Preferably, appropriate sensor circuitryand logic for this purpose is used in the meter interface logic 180 toenable the meter to be read with nearly zero power consumption,particularly in cases where the meter module 22 is powered by a limitedpower source, such as a battery.

A typical prior art sensor configuration is illustrated at 270 in FIG.17, and includes a switch 272 which is located in a meter 58 and has twooperation states, open (illustrated) and closed. The switch ispositioned to be activated periodically by a pin, or register, mountedon a rotating disk in the meter, in known manner. When the switch isopen the circuit from voltage source Vcc through conductor 274 to groundpoint 276 is broken and the voltage measured at the V-sense node 278equals the supply voltage Vcc. When the switch 272 is closed, thevoltage measured at the V-sense node is the circuit's ground levelreference voltage; i.e. zero voltage. Measuring the two electricalstates at the V-sense node 278 allows the two switch states open andclosed to be distinguished, with the periodic opening and closing inresponse to rotation of the disk providing a measure of utility usage.

Although most switches have finite conductivity, it is very low, and thetypical power consumption when switch 272 is in the open state isacceptable for long operating life. However, during the closed state,power is consumed at a level that may be significant when the energysource is limited, as with battery-powered devices, and when thatlimited source must remain operative for lengthy periods of time, as isoften the case with meter modules. In addition, the amount of energywasted in this way typically cannot be predicted, and may vary widelywith utility customer consumption patterns.

A preferred alternative to the sensor configuration of FIG. 17 may bereferred to as a “Zero Current Sensor Configuration”, and is illustratedat 280 in FIG. 18. This implementation is based upon a componentselection and geometrical arrangement of two sensor switches located inmeter 58, in which only one of the two switches may be triggered to aclosed switch state for any possible position of a sensed rotatingelement.

In meter configuration 280, two switches 282 and 284 are connected inseries with respective registers 286 and 288. These registers areactivated or deactivated by control commands from the controller module182 (FIG. 15) by way of logic interface 180 and connector 62. Loading ahigh state voltage from interface 180 into a meter register causesactivation of the associated switch 282 or 284, respectively. Loading alow state voltage into a meter register causes deactivation of theassociated switch 282 or 284. When a switch is deactivated by itsregister, no current can flow through the switch, even when the switchis closed. When no current flows, no energy is wasted, and this occurswhen the switch is open, or when the switch is de-activated by itsregister, without regard to whether it is open or closed.

The controller module 182 is programmed to deactivate one of the twosensors through logic 180 by deactivating a sensor register as soon as aclosed switch state is detected in that sensor. In addition, thecontroller module immediately activates the other sensor through itsregister. For example, if switch 282 is open and register 286 initiallyhas a high voltage state, then switch 282 is activated, but open. Whenthis switch detects a predetermined condition, such as a projectionelement (magnet/reflector/pin) on a meter rotor, it changes its statefrom open to closed, and the voltage at node 190 (V-sense 1) is changedfrom the high state voltage of register 286 to zero. This voltage dropis detected by interface 180 which wakes up the controller module 182.The controller then deactivates switch 282 by loading a low statevoltage in register 286, and at the same time it loads a high statevoltage in register 288 to activate the open switch 284. This latterswitch is located in a different projection zone than switch 282, andsince switch 284 is open, no current flows. Since switch 282 is nowdeactivated, no current flows through that switch either.

When the rotation of the meter disk or wheel continues and theprojection element reaches the projection zone of switch 284, it changesits state from open to closed, the voltage at node 292 (V-sense 2) ischanged from high state voltage to zero, and the controller unit 182 isawakened and immediately deactivates switch 284 and activates switch282. One rotation of the disk or wheel is defined as a state change ofswitch 282 from open to closed, followed by a state change of switch 284from open to closed, after which the controller 182 increments the meterrevolution count. Since neither switch is ever active and closed in thisconfiguration, the continuous current drain of the sensor circuitry onlyincludes that of the open switch, which is near zero.

Although the invention has been described in terms of preferredembodiments, it will be understood that numerous modifications andvariations may be made without departing from the true spirit and scopethereof, as set forth in the following claims:

1. A method of encoding interval consumption values transmitted by ameter module in a metering data collection system, comprising:collecting consumption values at selected intervals by a processor;compressing the collected consumption values using a logarithmic tableencoder to reduce the number of bits required to transmit theconsumption values collected at the selected intervals over a period oftime; and specifying one of a plurality of logarithmic encoding tablesto compress the collected consumption values, based on an expectedconsumption pattern at the meter module.
 2. A method of increasing theredundancy level of interval consumption values transmitted by a metermodule in a metering data collection system, comprising: transferring aplurality of the interval consumption values collected at selectedintervals over a time period from said meter module by a transmitterusing multiple messages related to the same time period, each of saidmultiple messages having a time base; and shifting a time base of eachof the multiple messages related to a first time period compared to theprevious message related to the first time period, and shifting a timebase of each of multiple messages related to a second time period, inrelation to each other, in a cyclic manner with respect to correspondingsaid multiple messages related to the first time period.
 3. The methodaccording to claim 2, wherein each of the multiple messages related tothe same time period includes samples of the interval consumption valuestaken at different sub-intervals within the same time period.
 4. Themethod according to claim 2, further comprising: compressing intervalconsumption values included in each of the multiple messages based on alogarithmic encoding table.
 5. A method, implemented by a meter modulein a metering data collection system, of encoding interval consumptionvalues transmitted by the meter module, the method comprising:collecting interval consumption values at selected intervals over aperiod of time by a processer; selecting one of a set of logarithmicencoding tables assigned for use; compressing a plurality of thecollected interval consumption values for the period of time using theselected one of the logarithmic encoding tables to reduce the number ofbits required to transmit the interval consumption values for the periodof time.
 6. The method according to claim 5, the selecting including themeter module re-selecting a logarithmic encoding table from the set oflogarithmic encoding tables at each of at least two sub-periods of timewithin the period of time.
 7. The method according to claim 5, theselecting one of the set of logarithmic encoding tables including themeter module building a consumption profile for each of the set oflogarithmic encoding tables, comparing a corresponding consumptionprofile for each of the set of logarithmic encoding tables with anactual consumption profile based on the collected interval consumptionvalues, and selecting one of the set of logarithmic encoding tablesbased on the comparison.